BIOL 1441 1st Edition Lecture 4 Outline of Last Lecture I Facts about water II Properties of water Outline of Current Lecture I Moderation of temperature continued II Expansion upon freezing III Universal solvent IV Section 3 molecular mass V Section 4 pH Current Lecture I Moderation of temperature continued a Evaporation liquid to gas i Liquid molecules all attracted to each other molecules start moving fast enough break all bonds depart the liquid into the air as a gas ii Temperature AVERAGE kinetic energy of molecules iii Have some molecules moving fast even at low temp iv Heat liquid providing energy average kinetic energy increasing quicker b Heat of Vaporization Quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to gas state i Water has a high heat of vaporization These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute ii H2O needs a lot of heat to vaporize iii H bonding Must break all those bonds 1st iv Evaporate 1 g H2O at 25 C you need 580 cal of heat v Heat of Vaporization significance 1 Moderate Earth s climate 2 Tropical seas absorb a large amount of solar heat 3 Water evaporates moist warm tropical air 4 Warm air circulates poleward releasing heat 5 Lose heat forming more H bonds 6 Gas liquid RAIN vi Surface water that is evaporating highest kinetic energy hottest c Evaporative Cooling avg temperature drops i Contributes to the stability of temp in lakes and ponds ii Prevents terrestrials from overheating iii Water evaporates from plant leaves prevents tissue from becoming too warm in sun iv Sweat cools you off evaporates off of your skin dissipating your body heat 1 High humidity is hotter why because already so much water in the air cant come off of your skin II Expansion Upon Freezing a Water is less dense as a solid ice than a liquid b Solids have more molecules packed tightly together c More mass heavy d So why is water lighter as a solid i Water expands instead of contracting below 4 C ii H bonding e Behaves like other liquids when at 4 C or above f Expands as it warms g Contracts as it cools i Below 4 C behaves very uniquely 1 Starts expanding 2 Water is densest at 4 C ii Freezing molecules are no longer moving vigorously enough to break Hbonds 1 0 C water locks into a crystal lattice each molecule bonds to 4 partners 2 H bond set distance apart 3 Ice 10 less dense than liquid 4 water at 4 C 10 fewer molecules for same volume 5 If ice sank life as we know it would cease to exist a All ponds lakes and oceans would freeze solid b Summer thaw only the upper few inches of the ocean c All the animals burrowed into sediments die III Universal Solvent a Solution liquid that is completely homogeneous mixture of 2 or more substances i salt water salt dissolves and the concentration is then uniform throughout the water b Solvent dissolving agent water c Solute substance that is dissolved salt d Aqueous solution water is solvent i NaCl ionic compound Na cation Cl anion ii Surface of salt crystal charges iii Attracted to water charge iv Oxygen attracted to Na v Hydrogen attracted to Clvi Water molecule surrounds 1 individual Na or Cl ions e Sphere of water molecules i Hydration Shell ii Separates them shields them from one another f Compound does not need to be ionic to be dissolved i Nonionic polar molecules sugar molecules ii Ionic compound each individual atom has a charge iii Nonionic compound atoms have no charge iv Polar molecule charge difference throughout the molecule g Hydrophilic Hydrophobic Substances i Hydro water Phiolios loving ii Hydro water Phobos fearing iii Hydrophilic any substance with attraction to water charges 1 Ionic or polar substances 2 Dissolve in water 3 Some large molecules inside of cells do not dissolve remain suspended in liquid portion of the cell a Colloid stable suspension of fine particles in a liquid i EX Cotton 1 Cellulose very large molecules with regions of partial charges 2 Water will adhere to cellulose 3 Cotton will absorb water well 4 Cotton towels t shirts good drying iv Hydrophobic 1 Nonionic nonpolar substances repel water 2 Olive oil nonpolar bonds no charge share electrons equally 3 Cell membranes hydrophobic v Like Dissolves Like 1 Charged molecules attracted to charged molecules a Hydrophilic molecules i Ionic substances ii Polar molecules polar covalent bond 2 Uncharged molecules attracted to uncharged molecules a Hydrophobic molecules i Nonpolar molecules nonpolar bonds ii NO charge IV Section 3 Molecular Mass a Almost every chemical rxn in your body occurs in H2O b To understand these rxn s we must know how many atoms molecules are involved i How many molecules are in this solution ii Use mass to determine number of molecules c Molecular Mass i We know the mass of each atom in a given molecule ii Mass of atom protons neutrons atomic mass d Molecular mass sum of the masses of all the atoms in a molecule i H2O 2 hydrogen atoms 1 oxygen atom 1 H2O molecular formula ii Sucrose table sugar 1 Molecular formula C12H22O11 iii Determine mass each atom 1 C 12 daltons 2 H 1 dalton 3 O 16 daltons iv Mass x number of atoms in molecule 1 Carbon 12 dal x 12 atoms 144 dal 2 Hydrogen 1 dal x 22 atoms 22 dal 3 Oxygen 16 dal x 11 atoms 176 dal 4 1 molecule of sucrose 342 daltons v Moles 1 342 daltons can t weigh that out 2 Use conversion Avogadro s number a Mole mol 6 02 x 1023 molecules b 6 02 x 1023 daltons in 1 gram c 1 mol sucrose 342 g MOLAR MASS d 6 02 x 1023 sucrose molecules 342 g 1 mol e 1 mol 6 02 x 1023 molecules Quantity f 6 02 x 1023 daltons 1 gram Weight g 6 02 x 1023 molecules x 342 daltons x h 1 molecule 1 g 342 grams 6 02 x 1023 daltons i 1 sucrose molecule 342 daltons j 6 02 x 1023 molecules x 342 daltons 2 06 x 1026 daltons 3 2 06 x 1026 daltons x 1 g 342 g 4 6 02 x 1023 daltons 5 1 mol molecular mass g 6 1 mol of any substance molecular mass g 7 Need 1 mol of water how much do you weigh out a What is the molecular mass of water 18 daltons b Answer 18 g water 1 mol i Water 1 mol 18 g ii Sucrose 1 mol 342 g iii Ethyl alcohol 1 mol 46 g vi Molarity 1 Molarity number of moles of solute per liter L of solution a Make 1 molar 1 M aqueous sucrose solution b 1 L with 1 mol sucrose in water c 342 g sucrose up to 1 L of water vii Terms 1 …